In contrast to all of the substrates currently being used to measure serum acid phosphatase levels as an aid in the diagnosis and confirmation of prostatic cancer, it appears that phosphoryl choline may have a truly unique specificity vis a vis hydrolysis by the prostatic enzyme. It is proposed to test possibility in the clinical laboratory by making measurements of acid phosphatase levels in serum samples by one of the currently-used conventional methods and also with the use of choline phosphate as a substrate. The results will be compared for the extent of correlation of the two methods with confirmed cases of prostatic cancer.